Drop-on-demand ink jet printers use thermal energy to produce a vapor bubble in an ink-filled chamber to expel a droplet. A thermal energy generator or heating element, usually a resistor, is located in the chamber on a heater chip near a discharge orifice. A plurality of chambers, each provided with a single heating element, are provided in the printer's printhead. The printhead typically comprises the heater chip and a plate having a plurality of the discharge orifices formed therein. The printhead forms part of an ink jet print cartridge which further comprises an ink-filled container.
The resistors are individually addressed with an energy pulse to momentarily vaporize the ink and form a bubble which expels an ink droplet. A flexible circuit may be used to provide a path for energy pulses to travel from a printer energy supply circuit to the printhead. Bond pads on the printhead are coupled to end sections of traces on the circuit. A plurality of first and second conductors are provided on the heater chip and extend between the bond pads and the resistors. Current is delivered to the resistors via the traces, the bond pads and the first and second conductors.
In first generation printheads, the number of first conductors and associated bond pads equaled the number of resistors provided on the chip. However, fewer second conductors, each coupled to two or more resistors, were provided. The first and second conductors were located in generally the same plane as the resistors.
In order to reduce the number of first conductors and associated bond pads, later printers and printheads were provided with decoder circuitry. Decoder circuitry, however, is expensive and, hence, undesirable.
Accordingly, there is a need for improved structure within an ink jet printhead for providing energy pulses to heating elements.